The face-plant I'm referring to usually occurs when the toddler is bending down to retrieve something, or when getting up from the ground. It's that perilous position, with hands and feet on the ground, head down that does them in. Their proportionally huge noggin pulls them past the point of balance, to a place from which there is no pleasant return--the face-plant.
Big fell on the sidewalk while he was outside with Rophone, with no apparent injury....until he tried to get up. That big head just pulled him over, so now he looks like this:
He seems to have recovered for the most part. I'm sorry your head's so big, Big!